text:
How strict is the relationship between ATC departure gates and SIDs?
I'm training to be an ATC on VATSIM, and the term "valid departure gate" is tossed about a lot, but not (to my perception) defined.  Googling "departure gate" drowns me in passenger terminal maps and notes about what TSA will make me throw away before being allowed to board my plane.
This question about 'arrival gates' seems to clear that up, but since my first role on VATSIM will be verifying that routes are kosher as Delivery controller I wan to be as clear as possible:
Is a departure gate always the final fix on a SID/Transition? Or should I be double-checking additional fixes along the route (when there's no preferred route to check against) to ensure that they're crossing from our center to another center correctly?

Departure gates are defined in the Letter of Agreement (LOA) between the approach control and the enroute facility (ARTCC). The LOA will define which aircraft are required to be routed through the departure gate (not all departure aircraft are necessarily required to be routed through the gate). Departure gates are normally drawn on the LOA annex on the approach control/ARTCC boundary and are typically 10-15 miles in length, although that can vary from LOA to LOA.
Enroute automation (ERAM) will normally be adapted to revise the route of flight for departures that are not filed through a gate, reducing controller workload.

So that sounds like "They're not strict at all, they have nothing to do with each other except by coincidence," if I read you correctly?

Whether a SID and a departure gate have anything to do with one another depends on the operation. At medium sized airports with an associated approach control, departure gates may be required and they may coincide with the SIDS. At large airports, gates aren't used much because the LOA says something like,  "all aircraft will be established on an RNAV SID or vectored through a departure gate." Since almost all airliners are RNAV equipped, the departure gates get used very infrequently.

The gate is usually the last (departure) or first (arrival) fix that is shared between all the transitions, which is the end of the “basic” SID/STAR.  The gate is often itself listed as one of the transitions, and such a procedure is typically named after its gate.
There are also some SIDs/STARs that don’t have a “basic” section; the textual description will say to expect radar vectors to/from the first fix on your transition, which is probably your gate. Such a procedure is typically named after the airport itself, a VOR near the airport, or something else that obviously isn’t a gate.
Either way, gates are usually on the border between facilities, which can help identify where those boundaries are if you don’t already know.
But there are always exceptions, so if you have specific examples in mind, please add that to your question.


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Can aircraft in formation shoot instrument approaches as a formation?
Formations taking off and landing together is obviously a thing in VFR, but I'm curious if these operations are possible/remotely safe when the formation is flying in IMC.
Example: A two-ship flight of Cessna 172s is nearing their destination airport on an IFR flight plan. The airport's ATIS says to expect an ILS approach.
Can the formation shoot the ILS approach together, or do they need to breakup the formation and then get sequenced individually?
If the latter, when is the best time for the break to occur? (I'd assume either before or after you get handed off to Approach.)

To build off this, under what circumstances is IMC formation flight NOT possible? It has to be reeeeeeally foggy on the ground for visibility to drop below 1/4 SM vis, for example—are all clouds at that uniform level of fogginess? How close together are typical aircraft in formation? Etc.

Related: https://aviation.stackexchange.com/questions/96772/what-are-the-constraints-and-procedures-regarding-imc-formation-flight

@MichaelHall Nah that was good enough for our purposes.  Sim crashed just before we established on the localizer anyway. >.>

Sure, that is in fact, one of the justifications for training military pilots in Formation approaches and landings... To lead an aircraft with an emergency down to a safe landing in IMC conditions when their emergency would otherwise prevent them for executing an instrument approach on their own (instrument failure, or electrical failure, etc.).
But just to comply with an ATC instruction to shoot an ILS approach (assuming both aircraft are ILS capable), would not seem appropriate to me.
... and, before someone else points this out, this is an inherently, potentially risky procedure, which requires a great deal of training and proficiency. It should not be attempted without both.

My practical needs are in a simulated environment, so the safety issue is mitigated, but I'm far less interested in simulating something that would basically never come up IRL, so thank you for the context.  What sorts of minima are needed for IMC formation operations of this sort?

This raises an interesting issue of how training could be done.  IFR training is generally done with vision limiting devices (Foggles etc) so the trainee can only see the instruments.  Formation flying is all about visual separation from the lead aircraft.  You could not safely train for formation flying while your outside view is restricted.

@Adam, the required skill sets between lead and wingman in IMC are as different as night and day.  Lead is all about being the smoothest and best instrument pilot they can be, while the wingman just needs to hold position.  Really zero instrument scan at all sometimes for the wingman, occasional quick peeks inside for awareness when you can loosen things up.  So yeah, no view limiting device!

Clearly, the wingman performing a formation approach and landing in IMC is not operating under IFR (Hopefully his/her flight leader is). It might be said that he is operating under FFR (Formation Flight Rules?) He is almost 100% outside the cockpit, flying with reference to the lead aircraft.

As to weather minimums, it has been 35 years now since I did this, but to my recollection, there were no distinct weather minimums for performing a formation approach and landing. The published weather minimums for the approach itself governed whether the flight leader could perform the approach. It did not matter if he had a wingman, or not.

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What CTAF/phraseology should be used for non-airfield departures?
Assume a pilot has landed their aircraft on a body of water in a lightly populated area, though the question still holds for large grassy meadow. The time has come for them to depart.
They're not on an airfield, per se, but there are airfields in the area at various distances and of various degrees of business.
While I'm sure it's perfectly legal to simply get airborne and go blasting into the sky... As a matter of safety and courtesy: on what frequency and using what phrasing should the pilot announce their departure and intentions in case someone else is contemplating an approach to the same site they're departing from?
If specifics are required, assume the pilot is flying an ICON A5 out from Lake Keowee in Salem, SC.

I'd lean toward using the CTAF at LQK (122.8) or CEU (119.27). Especially CEU if you'd be operating on the sourthern portion of the lake within CEU's Class-E-at-700'AGL circle.

"Lake Keowee traffic, ICON A5 taking off to the North, Lake Keowee..."

@randomhead The flight I'll be simming this evening involves overflying the Oconnee Nuke so that's a good thing for me to keep in mind, thanks!

I presume you’re talking about a lake or a body of water, or a off field landing site commonly used by aircraft, but not identified as an land or water airport or helipad as such on aeronautical charts and publications.  In these situations, it would be good practice to use the MULTICOM frequency of 122.9 to announce your position and intentions as prescribed in AIM 4-1-9.  Pilots approaching or egressing from such areas may use the air-to-air frequency 122.75 or 123.05 (for helicopters).  Groups of aircraft entering or egressing here areas may also communicate on ‘fingers’ frequency of 123.45 as well.
Organizations like the Seaplane Pilot’s Association also publish commonly used procedures and information on popular water destination for seaplanes.

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Is there a minimum density a cloud must attain before it is, legally speaking, a cloud?
I was doing a simulated tour of local untowered airfields the other day, operating VFR on VATSIM in Class B airspace (Logan).
Whenever I'm in Class B as a VFR flight I like to give ATC as boring a radar target as I possibly can. Obviously, as a VFR flight, I'm instructed to maintain "clear of clouds."
It was scattered clouds just above me at the altitude ATC put me at, but as I was getting near the coast they were getting lower - but nothing near me...until suddenly there was.
The cloud I encountered was about eight times the size of the Cessna 152 I was flying. I elected to plow through it, justifying the choice by the fact that I could easily see the terrain and other clouds on the far side of it - I could see right through it (it was more of a mist, really). But even at the time I recognized that it was entirely possible for me to miss a steel-grey-against-grey-clouds aircraft because of the visual noise. I wound up clipping through the top quarter of it; the transit lasted about three seconds. I never lost visual reference to the ground.
Is that legally VFR? Should I have diverted around it to maintain fully clear of anything that might possibly be construed as a cloud?
And relatedly, if I do have to divert... do I need to inform a busy Class B approach controller that I'm about to depart from the altitude he put me at in order to maintain clear of clouds?

"I wound up clipping through the top quarter of it" -- the cloud or the steel-gray aircraft? :)

@nanoman The alleged cloud. :)

I feel like you might be describing vapor instead of a cloud. I don't know if there's a formal FAR definition for "vapor", but it stands to reason that if visibility doesn't drop below VFR minimums that the water mass is not technically fully "visible".

An interesting thing to consider is what about if visibility on the ground is barely above minimums due to light haze/fog. I can still takeoff.  From above that haze/fog layer it might look  a bit like a cloud.

To answer the question in the title,

A cloud is a visible aggregate of minute water droplets and/or ice particles

per FAA AC-006B, page 105.  If you can see it, it's a cloud.
More practically (not a direct FAA quote; I didn't find chapter and verse),
VFR visibility minimums

...state a specific visibility distance requirement and a specific distance separation from clouds. Visibility through clouds varies by the angle of the view... while you may be able to see through a specific cross section of a cloud you're approaching, IFR traffic elsewhere in that cloud might not see you.

(Page 139 of the AC distinguishes clouds from rain:

Precipitation is any of the forms of water particles, whether liquid or solid, that fall from the atmosphere and reach the ground. The precipitation types are: drizzle, rain, snow, ...

Although the AC doesn't specifically define that a cloud does not "fall from the atmosphere," it draws a distinction between clouds and rain even more strongly by putting them in separate chapters.)

This answer employs flawed logic. Because the FAA defines what characteristics a cloud must have does not mean that everything with those characteristics is a cloud.

Reading further, FAA AC-006B does differentiate between clouds and fog.  Importantly, even if one is near clouds, RH may be dangerously high (and more may form).  Best to avoid them, particularly with approaching fronts, if flying VFR.

@KennSebesta Because FAA defines what characteristics a cloud must have, by the standard rules of legalese, does mean that whenever any of their document says cloud, it means anything and everything that has those characteristics.

@KennSebesta If the FAA had merely stated that clouds have certain characteristics, then your comment would be valid. But they actually defined clouds as being things with those characteristics, so your comment is invalid and the answer (and Jan Hudec’s comment) is valid.

I'd say it's pushing the meaning of the term to call raindrops "minute".  They're big enough to be seen individually by the naked eye.  And yes at some point there could be a droplet that just barely big enough to fall but still so small you couldn't pick it out, but that's inevitable when using language to describe a continuous world.

@JanHudec I hadn't realized there were legalese standards, thanks for the clarification. I'm not fully convinced that the FAA would/could distinguish between vapor and a cloud, but I follow your reasoning.

Your quote from page 105 of the AC partially reads, “…while you may be able to see through a specific cross section of a cloud you're approaching, IFR traffic elsewhere in that cloud might not see you.” That’s an important consideration. It is, after all, “see and be seen”. You can’t always control that, but there ARE things you can do.

No - there is no minimum density needed to meet the definition of a cloud, only that it be visible and consist of liquid or frozen water.
Meteorologists may care about actual cloud density as it relates forecasting rainfall, but pilots only care about the effect of density on visibility.
The minimum visibility for flight under VFR (in most US airspace) is three statute miles.  Three statute miles is actually very poor compared to a day when visibility is unlimited.  It is possible to fly in conditions where an area of reduced visibility exists due to “a visible aggregate of minute water droplets and/or ice particles”, (The FAA definition of a cloud) but that visibility within this aggregation could exceed 3 statute miles.
The purpose of cloud clearance requirements is to provide safe separation between VFR traffic and IFR traffic operating in IMC.  While the requirements only mention “clouds”, clearly the intent is to avoid cloud formations within which the visibility is below VMC, not that you “avoid anything that might possibly be construed as a cloud”.
The rules state to avoid clouds because 90+% of the time visibility is reduced because of… clouds.  However, whether an area of IMC is due to clouds, smoke, dust, haze, volcanic ash, or any other atmospheric phenomenon, if visibility is less than 3 miles you should avoid it if you are VFR.
Conversely, if visibility is greater than 3 miles there is nothing restricting you from transiting under VFR, regardless of the composition.
In short, the adage “if you can see through it you can fly through it” is generally accurate enough.

In UK air law the wording is ‘in sight of surface’ so provided you can make out any part of the terrain to your own satisfaction you’re in VFR.


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Current Status of MOSAIC
MOSAIC (Modernization of Special Airworthiness Certification) is a cluster of proposed FAA rule changes that would broaden the aircraft eligible to be operated by a pilot with a Sport License. In July of 2023 they issued a Notice of Proposed Rulemaking (NPRM), the initial step in the promulgation of new regulations.
The comment period (typically 30-60 days) was extended to the end of January, 2024 and is now closed.
It has now been six months since.  I'm accustomed (as a policy scholar) to final rules being produced within 30-90 days of the closure of comment periods, with rules going into effect 30-90 days after publication of the final.
What is the current status of MOSAIC, when should we expect a final rule to be published, and did I miss a confirmation notice being published somewhere?

MOSAIC received a lot more public feedback than many NPRMs, so it is not surprising that it is taking longer.
As far as I know, no timeline for the final rule has been announced publicly. A spokesman for the EAA has claimed that people at the FAA told him in conversations that they expect a final rule in early to mid 2025.
The FAA reauthorization act mandates that the final rule be issued no later than 24 months after the passage of that bill. That bill was passed on May 16, 2024, which puts a hard deadline of May 16, 2026 for the MOSAIC final rule. But hopefully it's earlier!


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How Ready for a 2031 TEL ban Is The Avgas-Fueled Fleet?
Per this article on AvWeb, California has codified a full-on cold-turkey ban on leaded avgas effective January 1st, 2031.
Obviously there's more than six years between now and then, but what is there left to do for the avgas-fueled fleet to be unleaded-ready by then - as of today (October 2nd, 2024)?
What proactive measures can pilots and owners take to ensure their operations aren't disrupted?

The article also says "But if the FAA misses that deadline, the bill, as passed, will still ban leaded avgas the next day."

@PeterGreen: GAMI already proposes G100UL for TEL-free fuel compatible with 100LL engines (in addition of 94UL and 91UL which can also be used in many 100LL engines with an adapter), and EU has already planned to completely sunset TEL in may 2025 for any fuel, 5 years before FAA. Anyway if there were no solutions, then the bill would just be repealed.

@mins Not California. They'll ban piston planes first.

@mins -- California could just yanno, start buying G100UL directly by the tankcarload and shipping it out to airports themselves lol

@UnrecognizedFallingObject: It seems they already planned for a distributor "GAMI partnered with Avfuel Corporation through Avfuel Technology Initiatives Corporation (ATIC) to oversee logistics and distribution. Avfuel is a global supplier of aviation fuels and services, and currently sells 100LL to more than 675 FBOs" (source)

@user71659: "Not California. They'll ban piston planes first". You could be wrong: Aircraft operators in California will likely be the first to be able to fill their tanks with unleaded 100 octane aviation fuel and that will be GAMI fuel.

@mins -- it seems that 94UL is the closest thing available so far if Livermore's fuel selection is indicative

@UnrecognizedFallingObject: If you read the article: "The phase out of lead won’t be complete until 100UL is available everywhere 100LL is sold today; that rollout process will probably take several years.". Hopefully this will be less than 5 years. See also the paragraph "Will 100LL be banned before G100UL is widely available?"

@mins -- the article you linked is from Feb.

The fleet is 100% ready, because the point of a drop-in replacement is that it can be used as a substitute without any modifications whatsoever. It's not the fleet that has to be ready, it's the fuel which has been the tricky part. At this point the status of the readiness for the drop-in replacement is debatable and I will not go over it here, although I would say that the available options would seem to fit the bill for the vast majority of engines.
Having a fuel formulated and tested is one thing, having it mass-produced and distributed is another, what pilots and owners can do (no matter where they are) is pressure governments to get their acts together, and where the bans are going to be in place to make sure their local airfield operators are on the ball on getting the fuel.

Yeah, G100UL seems to be more or less a drop-in substitute for most aircraft AFAIK (the STC is paperwork and placarding, similar to a Peterson mogas STC, at least AIUI).  The problem is actually getting your hands on a 55gal drum of the stuff, as the distribution chain seems to not want to touch it with a 10' pole.


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A321 XLR or A321NXLR
Wikipedia says that the A321XLR, will entering service in 2024,but when you look at Airfleets. net, TAP Portugal has already serval A321NXLR in use, or is this a different Model? how many Variants of the A321neo are there and what X stands for?

The labels used on airfleets.net are indeed a bit confusing. Other sites write for example "A321-251NX/LR" to distinguish the "NX" from the "LR" part. Here is what everything means:

N is added for all neo variants
X refers to the Cabin Flex option that allows airlines to configure different emergency exits
LR is the Long Range variant of the A321neo
XLR is the Xtra Long Range variant of the A321neo

So the TAP Air Portugal aircraft are A321 LR aircraft with cabin flex, not XLR. The XLR should enter service later this year (2024). I don't know how airfleets.net will show this variant, but it should probably be something like "NX/XLR".
More on Cabin Flex:

From the Airbus Newsroom in 2018:

The A321neo in Cabin Flex configuration is an option today and will become standard for all A321neos around 2020.
The A321neo in Cabin Flex configuration is also the base for a longer range variant known as the A321LR.

Related question: Which category is A321-271NX in?


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Gear down on climb out
i saw on a live stream from Manchester, that a Virgin A330, left the landing Gear down for 2-3 Minutes after take off, a smiliar scenario i saw on a stream from Heathrow, where British Airways and Virgin 787s,left the gear down for a while, a Chatter said hot breaks, but how is this possible on take off?

Welcome to aviation.stackexchange.com. I am sure this question has be answered before on this website.

See  "Why would a pilot leave the gear down after takeoff for extended period of time" and "Why did my flight leave the gear down for the first 10 minutes of flight? duplicate"


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Landing gear: why is there a maximum altitude for safe retraction?
According to this article, the Dash 8 has a "maximum altitude for safe retraction".
This wording implies that there is some danger of retracting the gear above a certain altitude. Is this the case, or was this just sloppy language and the danger is actually in flying above a certain altitude with the gear extended?
In either case, why does this safety limit exist?
Specifically:

What are the engineering reasons for this limitation?
What are the potential consequences of retracting the landing gear above this altitude (or flying too high with the gear extended)?

I feel that all three answers to date add constructively to the overall answer, and I have +1'd all of them. I'd be happy giving any of them the green tick, so I'll just choose the earliest.

You can find the actual ATSB report here and that information was pulled right from it, they are not mis-types:

The report goes on to state (bolded for emphasis):

The operator advised that, although the maximum landing gear altitude
limit was exceeded, the aircraft maintenance manual did not require an
inspection of the landing gear. The manufacturer confirmed that an
inspection of the landing gear was not required. It stated that the
15,000 ft altitude limit was a practical value, not a limiting value.
It was based on the normal envelope of landing gear operation. It
advised that the aircraft had been demonstrated above 15,000 ft with
the gear extended and confirmed the gear would operate normally above
15,000 ft. As such, no inspection was required.

The note likely landed in the manual due to the fact that gear can effect stall characteristics. Typically gear deployment and retraction limits are speed based in my experience.

The first paragraph of this answer doesn't seem right. You write "those quotes were indeed pulled right from it," which made me think that the phrase "maximum altitude for safe retraction" is a direct quote from the ATSB report, and therefore accurate. In fact, the opposite is true.

Is the idea that maintaining an altitude over 15,000 feet would generally require an airspeed of over 205 knots, which wold preclude operation of the gear, but that if e.g. the plane was at a nose-down pitch that was insufficient to maintain altitude but allowed airspeed to be reduced below 205 knots, then the gear could be operated regardless of altitude?

@supercat The report actually states: "A review of the recorded data for the flight confirmed that neither of the landing gear speed limits were exceeded."

This wording implies that there is some danger of retracting the gear
above a certain altitude. Is this the case, or was this just sloppy
language and the danger is actually in flying above a certain altitude
with the gear extended?

It appears that the article is indeed sloppy in its use of the phrase "maximum altitude for safe retraction". Later the article states "However, this was above the maximum altitude at which landing gear could remain extended, at 15,000 feet,".
If I were a pilot in an unusual situation, my likely actions would be very different if I thought I had exceeded the "maximum altitude for safe retraction", versus if I thought I had exceeded the "maximum altitude at which landing gear could remain extended".
Another answer has pointed out the reasons why the manual contains a statement about the maximum altitude at which landing gear could remain extended.  It appears that this pertains solely to what had been previously demonstrated in actual flight.  It seems unlikely that, for a given IAS, there would be any real problems associated with flying with the landing gear extended above the altitude limit that had actually been demonstrated in flight.
Though since flutter is a TAS-dependent phenomenon, and TAS (for a given IAS) increases with increasing altitude, and likelihood of flutter is also dependent on aircraft configuration, you never know.  Once you venture beyond the realm of what has been actually been demonstrated, you become a test pilot.  Not recommended when flying with passengers.

Any chance that extra cold air getting into the gear wells could be a problem?  (vs. the smaller amount of cold air with the gear up)?  I'm guessing not, since there's no relevant heat source nearby that would keep anything above ambient temp with the gear up; not like that's airtight and insulated.  And presumably the moving parts don't have a problem with the cold, or it would be a retract/extend limit, not a gear-out limit.

I should start with the remark that I have no flight experience or education whatsoever. But after reading the ATSB report I have a plausible theory about the limits.
Generally, limits for operating aircraft in their various configurations have one of two reasons: Exceeding them may damage components, or exceeding them leaves the proven safe flight envelope of the aircraft.
The listing of the "Relevant aircraft limits" in the ATSB report mixes limits from both categories:

The speed limit for gear operation exists because the forces on the landing gear can damage the gear or the hydraulics. It is lower than the maximum speed with lowered and locked gear because the gear is, unsurprisingly,  mechanically more stable when locked. If the landing gear is operated above this speed limit there is a danger of mechanical damage. Therefore an inspection is mandatory.
Whether the higher air speed for flying with gear extended indicates a mechanical limit or would lead to unsafe aerodynamics isn't obvious.
The altitude limit, by contrast, is almost certainly not a mechanical limit. The aerodynamic forces on the gear are actually lower than at ground level. The manufacturer's response indicates that it was simply an arbitrary upper threshold. That plane configuration was never verified at higher altitudes, because there was no need.1 Because the limit does not indicate a component limit there is no need to inspect the component when it is exceeded.

The article, as quiet flyer already observed, is sloppy and conflates "operating" with "being extended".
The confusion of categories with the mixed listing leaks into the aftermath considerations whether an inspection is necessary. (It is unclear to me from the passage in the ATSB report whether the ATSB initiated this discussion or whether the ATSB merely reports the communication between operator and manufacturer.)

1 Similar to a new medical drug: If it has never been tested on 5-year-olds it cannot be approved for them, even if there is no indication that it would be harmful.


text:
What instrument approaches can be flown with just a single VOR receiver?
I've been getting ready to do a series of streaming sessions on Microsoft Flight Simulator 2020 that demonstrate the extreme limits of IFR capability.  With stuff like the G1000, the Cessna 172 will readily fly itself all the way to the runway if you let it, which is great for safety but not terribly exciting to fly.
There's two aircraft in particular that seem to be barely IFR capable, and I'm interested in flying them IFR.
The Cessna 152 doesn't have any glass in it, just the old school paired nav radios with VOR instruments (and a separate ADF radio) - it doesn't even come with DME even though the real thing usually does.  I've sorted out how to locate myself using two VORs, and there's obvious approaches I can fly without DME. The ILS/LOC RWY 11 at Portland, Maine, for example, lets you substitute using the 2nd nav radio to detect various fixes by referencing the Kennebunk (ENE) VOR.
Enter the Robin DR400/100 Cadet - which has only a single nav radio/instrument.
I'd love to really stress-test IFR flight in the thing, but I have no idea how to even look for an approach (precision radar aside) that would be available to such a craft.  Is that plane basically vectored visual approach or bust? Or is there something I'm missing when looking at approach plates?

I've yet to see a C152 with a DME. One working VOR is usually it.

An approach where the VOR itself is your FAF & the MAP is defined by timing would work. Or a teardrop... fly out 1 radial for a defined distance (i.e. time), turn to intercept another radial inbound, then once established you can descend to your MDA; the station is your MAP.
Don't know offhand where such approaches still exist today; they're probably less plentiful now than in times before widespread adoption of GPS.

A good example of the approach you described is the VOR RWY 6 approach at KHQM. The HQM VOR is the IAF, fly outbound, procedure turn back on the same radial inbound, the VOR is then the also FAF which starts a timed segment to the  MAP. If you have a DME or GPS (but not required) you can identify the fix TEYKU and decrease minimums by 120'.
I flex this approach half a dozen times during training just because it represents a very equipment minimalist procedure.


text:
1 in 60 rule for VORs
I'm working on some math questions for a CPL exam (not the FAA written), and I am curious about the 1:60 rule. How does that math work out? I know that if you're 60 NM from the station and 1 NM off course, you're 1 degree off course. How does this work out for other angles? I'm also wondering if this is the same rule used to derive the VOR time/distance formulas.
Any insight would be helpful, along with derivations of the formulas. I'm just having trouble picturing everything in my head.
Thanks!

This is a fairly basic question of trigonometry. Imagine a very long but narrow right triangle. Your starting position is the the one degree angle, and you have two very long, near parallel, legs leaving that point. The hypotenuse is the 60NM route you actually fly, and the leg leading to the right angle is the route you planned to fly. The third short leg is the distance between your actual position, and your intended position, in your example, about 1NM.
What we need to do is find the length of the short side opposite the given angle. We have the given angle, and the length of the hypotenuse. This relationship is defined by a mathematical function called the "sine".
For example, we can take the sine of 1 degree, and multiply it by the 60 NM flown, to verify the 1:60 rule. We would plug $ 60 \, \text{NM} \times \sin(1°) $ into a calculator, and the result would be 1.05 NM - very close to the rule of thumb.
At small angles, the sine function is very nearly linear - double the angle, and you double the result. For example, if we use 2 degrees, we get 2.09 NM, and if we use 5 degrees, we get 5.23 NM. Even a 20 degree error leads to a deviation of about 20 NM off of your intended route after 60 NM flown. So, the rule of thumb seems to be useful within a pretty wide range.

"... of about 20 NM off your" seems like a typo? sin(20 deg)*60 = 20.52

So for very small angles you have $\sin (n°) \approx n / (180/pi) \approx n / 57.3$, but as the angle gets bigger that approximation is a little too high, so it makes sense to use a constant that's a bit bigger than 57.3.  60 has a lot of factors so it's easy to do the mental math.


text:
VMC Conditions for VFR flight
What does it mean by flight visibility of 5km and horizontal separation from cloud 1500m in VMC?
If a cloud is ahead of us at 1500m then how could the flight visibility be 5km?

Are you asking about a specific authority's definition, and/or in a specific class of airspace?

"Visibility" is taken to mean the farthest distance that can be seen in open air. It is affected by particles suspended in the air surrounding you, like smoke or dust or water vapor (mist/fog), or by larger precipitation falling through the air, like rain or snow.
Something like a tall building or a mountain or even a cloud being in your way does not count as a visibility obscuration. If you were inside the cloud then yes, the particles of the cloud would reduce the visibility. But when you're outside of the cloud you can treat it like a singular object.

"the farthest distance that can be seen in open air." Yet it is typically never reported greater than 10nm in the US, which actually isn't that great.  Also, maybe add the word "prevailing"?  Good answer BTW!

@MichaelHall Seeing what actual 10 mile visibility looks like for the first time is quite shocking! ;)

@chris, never more apparent than at sea, watching the tacan DME counting down and looking for "mom"...  You knew exactly what the visibility was.

@MichaelHall the automated equipment maxes out at 10 statute miles and usually there isn't a real reason to edit it. Good enough for government work. At manual stations like KMWN it's common to see visibilities of up to 100SM.

Isn't automation great?!  Anyway, maybe consider adding that to your answer and I will delete these comments to clean things up?

I think "visibility" just on its own means the farthest you can see in open air in any given direction. Prevailing visibility has a slightly different definition.

The cloud that is 1500m away from you could be to your side.  The 5km visibility standard is the farthest distance you can see.
The idea is simple, you need to be far enough away from the cloud so other traffic have a chance of not hitting you if you are hidden by that cloud.  I don't know what rules you are referencing but a VFR plane could be 500m below the cloud and be legal and you are 500m above them past the cloud.  When they look up, they will not be able to see you as you are obscured by the cloud.  If they were to rapidly climb once past the cloud they could potentially hit you.  The 1500m distance is designed to allow other pilots to see you with enough time to avoid hitting you.


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In a straight and level flight if thrust is equal to drag how is aircraft moving forward?
If two forces are equal and acting in opposite direction should not the object remain stationary.
Is there an excess thrust which actually pushes the aircraft forward ?

Per Newton's first law,

A body remains at rest, or in motion at a constant speed in a straight line, except insofar as it is acted upon by a force.

You need excess thrust to get up to speed. But once you are at your target speed, if you make sure there is no net force acting on the airplane by matching thrust to drag, the aircraft will remain in motion.

Similarly an object in space is neither experiencing thrust or drag (if no engines are firing and it's high enough above the atmosphere). So you could say that thrust equals drag (0=0), and yet the object continues in forward motion, affected only by gravity pulling from various directions.

Drag is produced by moving through the air- more speed means more drag. Thrust is the motive force that pushes the plane through the air- more thrust means more push.
At cruise, push equals drag and speed is constant- but not zero. Acceleration is zero in this case, not speed.


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Aircraft Intuitive Design Software
I came across a MATLAB app called "Aircraft Intuitive Design" by Zac Lietzau:
https://www.mathworks.com/matlabcentral/fileexchange/66770-aircraft-intuitive-design-aid
It allows the user to see the changes made to the geometry reflected in the stability and aerodynamic characteristics in real time.
It also computes the profile drag coefficient, as seen in the image below (Drag: CD = 0.047 (profile) + 0.057CL^2 (induced)):

I know induced drag can be calculated using vortex lattice methods, but I want to understand how the profile drag is being calculated. (I am unable to access the code)

Why can’t you download the code and read it?

This seems to be a question about one particular software package, rather than about Aviation itself. Since this stack isn't about software, this question may be off-topic here.

It's written in the website:
"In addition to built-in, linearized stability approximations that are updated every time the aircraft model is adjusted, the program interfaces with the following software for more advanced analysis:
• Digital DATCOM – U.S. Air Force
• Tornado Vortex Lattice Method – Tomas Melin (KTH Royal Institute of Technology)
• AVL (Athena Vortex Lattice Method) – Mark Drela and Harold Youngren (MIT)"
It's simply using the empirical equations from the DATCOM.


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Fuselage contribution to pitching moment for a canard design
I am trying to calculate the pitching moment of a fuselage. I am currently looking into the Munk-Multhopp method. The equation for it are given as:

where,

The next step includes dividing the fuselage into sections and calculating the summation term.
My questions are:

For a design with a fore and aft wing, what is the definition of 'S'? Is it the total wing planform area (fore + aft wing) or just the main wing planform area?

Is there another way to estimate the pitching moment contribution due to the fuselage?

Chapter 4.2.2 of the USAF STABILITY AND CONTROL DATCOM should help.


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How to calculate velocity of air behind a propeller?
Background:
I came across this article by Gabriel Staples to calculate static and dynamic thrust of a propeller. In the derivation, it was assumed that the exit velocity is equal to the pitch speed of the propeller, a function of RPM and propeller pitch (inches). However, it was also mentioned that this assumption is far from truth in real life, so the final thrust equation derived was empirically corrected.
Question:
I want to know what will be the average airspeed behind the propeller (exit velocity), if the engine is not moving forward (static thrust). Is there a way to calculate it?
(I want to know this speed to calculate the effectiveness of control surfaces submerged in the propwash)

As engineer: calculate but do not trust results: measure them! Answers below may give you some estimates, but they assume a lot.

You want to look into hover momentum theory.
The induced velocity at a hovering rotor $v_i$ is:
$$v_i=\sqrt{\frac{T}{A}\frac{1}{2\,\rho}}$$
Where $T$ is the thrust and $A$ is the area of the disk, so $T/A$ is the disk loading.  $\rho$ is the air density.
After the rotor, the streamtube that passes through the rotor will contract and accelerate.  Eventually, it will reach a velocity of twice the velocity at the rotor.

So what you're saying is exit velocity=2*entry velocity? But then... How do we calculate this, how is entry velocity calculated? How do you get from rotor parameters to exit velocity?

Since the rotor is in hover, far above the rotor, the velocity is zero.  At the plane of the rotor, the velocity is v_i.  Far after the rotor, the velocity is 2v_i.  You calculate v_i (the velocity induced by the rotor) using the equation I gave -- which is in terms of thrust and area.

Yes, if you know the propeller dimensions and the thrust this propeller generates.
From this answer we can derive an equation which gives exit speed in relation to thrust:
$$\Delta v = \sqrt{\frac{8\cdot T}{\pi\cdot d_p^2\cdot \rho}}$$
This is only valid for the static case: Entry speed is assumed to be zero.
Nomenclature:
$\Delta v$ = exit speed in m/s
$T\;\,$  = thrust in N
$d_p\,$ = propeller diameter in m
$\rho\;\;$ = air density in kg/m³

Sorry for commenting on an old post but the two formulas don't "match" if you solve for A=πr^2.  Should 8T be 2T in the bottom formula? Thanks!!

@user9251544 If you use the prop radius, 2 is the correct constant. If you use the prop diameter (which I do here), 8 is correct.

There’s a good chance I’m doing a childish mistake here but I’ll ask again just in case…  If I replace d with 2r in your formula, shouldn’t I get the top formula? With d=2r, the denominator becomes π4r^2ρ so the fraction becomes  2T / Aρ instead of T / A2ρ given in the top formula, what am I missing? I’m asking because I tried the same numbers with both formulas and they give wildly different results. Thanks again for your time!!

@user9251544 Since there is only one formula in this answer, I guess you refer to the linked answer, which has three distinct ones and more within the text. The first two are the same, only that initial speed has been set to zero in the second. The second formula is reproduced here, solved for ∆v. If you replace d/2 by r in both, they will still be equivalent. Where is the mistake supposed to be? Don't forget that r² is d²/4, and the fraction under the root in the formula in this answer here should read 2·T / (π·r²·ρ).

Thanks for your patience and getting back to me. The two equations I'm referring to are the ones on this page only, one from you and one from Rob. We both agree that if you solve your equation with r=d/2, you get 2T / Aρ but Rob has T / 2A*ρ (his 2 is in the denominator and yours in the nominator). They should be the same, shouldn't they?

@user9251544 It helps to be precise. Now I see what you mean. Rob's induced speed is the added speed in the propeller plane whereas ∆v is the speed behind the propeller. ∆v = 2·v$_\text{i}$, as explained here

yeap it was a childish mistake, should have read everything more carefully, thanks again!!


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Giant RC Ground Effect Vehicle: How to determine the thrust required for takeoff from water
I am an aerospace engineering student, trying to design a large ground effect vehicle (GEV), and need advice/help to decide the thrust required for it to takeoff from the water surface.

The model looks similar to the GEV in the following videos (It has a reverse delta wing and a flying boat style fuselage, with a large horizontal stabilizer):

 and

The specifications for the model that I am designing are as follows:
Total Weight (including batteries): 16.28 kg,
Wing span = 2.3 m,
Wing area = 2.281 sq. m,
Wing Loading = 7.14 kg/sq. m,
Aspect Ratio = 2.32,
Estimated Cruise speed = 16 m/s.
It was suggested to me that, as a rule of thumb, a power-to-weight ratio of 170 W/kg is required for take-off from water. I want to ask what is the minimum amount of thrust that will be needed for this model to takeoff and fly (if high performance is not a requirement)
How do I calculate the thrust required (or what kind of motors I need) for this model to takeoff from water and fly?
Thank you

A lot depends on the location and shape of the step on the bottom of the fuselage relative to the center of gravity.

I have designed the step to be 8-9% of the beam and the Centre of Gravity is to be slightly ahead of the step (on a line 10 degree to the vertical at step). I used this based on the book "RC Model Aircraft Design" by Andy Lennon.

I once did take-off calculations for the Dornier Seastar and remember that there is a tradeoff with a rear step which allows for a smaller angle while planing, causing less drag while going over the hump and a more forward step which better allows to rotate for liftoff. Generally, thrust required over the hump increases with the keeling angle. That is the reason why early seaplanes had a flat bottom. However, keeling improves ride quality when planing in rough seas.

There were designs with several and retractable steps. A retractable step reduces drag in flight but also combines the benefits of a more forward and a more backward step when used properly.
I guess I cannot improve on the advice you got from books, so I post this as a comment rather than an answer which my rant clearly isn't.


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Air intake sizing for a Turbojet Engine
I am trying to design a UAV with a turbojet engine. The turbojet engine is already selected, and I want to calculate how big the air intake will need to be for this engine.
I have read that the size depends on the mass flow rate, Mach number of the flow and design Mach number of the engine, and the intake size is such that the flow speed can be reduced accordingly.
Is there a way to estimate the air intake size (area of the air intake front face)?

What's the engine? What else has it been installed in?

@RalphJ The engine is AL-PBS-350, it is for use on UAVs, UCAVs : https://www.pbs.cz/en/Products/Aerospace/Aircraft-Engines/Jet-engine-AI-PBS-350

Inflow mass = outflow mass?  Cruise would need less air in.  Some type of adjustable ramp could save drag.

Crosthwait, E. L., Kennon, I. G., and Roland, H. L., "Preliminary Design Methodology for Air -Induction Systems," Technical Report SEG-TR-67-1, Wright-Patterson AFB, OH, Jan. 1967 is, I've read, highly reccomended.

I would defer to asking the manufacturer of the engine. What do THEY recommend? At least as a starting point. And that engine is pretty beefy - 51kg. You're designing a relatively LARGE UAV.


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Bi-directional Conversion Between CAN and ARINC825: Software or Hardware Necessities?
community!
I'm delving into a project that necessitates the conversion of ARINC825 bus input signals to  CAN outputs, and vice versa, requiring CAN inputs to be converted back to ARINC825 outputs (my software only handles CAN inputs and outputs at the moment). This crossover has led me to ponder whether such conversions can be exclusively handled through software solutions, or if there's a definitive need for hardware integration to bridge these protocols effectively.
Additionally, I'm on the lookout for any existing solutions that cater to this specific requirement. Are there any off-the-shelf, plug-and-play systems designed to facilitate this type of signal conversion with minimal setup?
Your insights or experiences with similar conversions would be immensely valuable to me. If you're aware of any relevant software, hardware, or integrated systems, please share your recommendations.
Thank you in advance for your assistance and knowledge sharing!

It might be worth clarifying if the proposed solution is just for bench testing/non aviation use, or if it will be going up in an aircraft at some point since that will change the options a bit.

Thanks for bringing up that distinction @GremlinWranger. To clarify, the solution we're discussing will indeed be used in an aircraft. Looking forward to your insights with this in mind.

What do you mean with converting ARINC 825 to CAN? My understanding is that CAN is the electrical interface and ARINC 825 is the message format on top of it.

Thanks for you help @Rainer P. Basically, I have ARINC 825 inputs but my software currently only processes standard CAN messages. I also need to output data as ARINC 825 signals, but my software only outputs standard CAN. I'm unsure about any specific hardware requirements for ARINC 825 on top of the hardware to do this conversion.

Again, what conversion? What conversion hardware? Your signals are already CAN. The AIRINC 825 standard tells you which packet identifier means airspeed/altitude/etc. Thats all software and one abstraction layer above CAN.

Thanks for the ARINC 825 insight on software vs. hardware—very helpful. I'm still getting to grips with its nuances like predictability, bandwidth, and scheduling from a software standpoint.
Also, some of the hardware I'm interfacing with requires direct CAN signals, leading to my questions about conversion of ARINC 825 signals to CAN for these specific hardware needs. Perhaps I'm overly cautious, but I really want to map out the potential implementation challenges before committing to this project.


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Temperature change & Altimeter indication
Ref:  FAA Pilot's Handbook of Aeronautical Knowledge 2023 (faa-h-8083-25c)
Page 8-4, column 2, paragraph 3 (including figure 8-3) through page 8-5, column 1, paragraph 1.
As a background to my question, the statements on Page 8-4, column 1, paragraph 3 through column 2, paragraph 1, related to flying from a high-pressure area to a low-pressure area without adjusting the altimeter make perfect sense (it is implied that the pilot maintains the plane’s indicated altitude in the process).  Clearly, the atmospheric pressure drops in the process and, as a result, the true altitude decreases if constant indicated altitude is held constant.  Said another way, if the true altitude were maintained in the process, the altimeter would display a higher indicated altitude as it would register the lowered atmospheric pressure.
By similar logic, I would think that traversing from a warm air mass to a colder air mass would result in entering into a denser air mass.  A denser column of air would therefore produce increased atmospheric pressure.  If one were to maintain the same indicated altitude during that part of the flight, I would think that the true altitude would increase.   Similarly, increased atmospheric pressure would show a lower indicated altitude if a constant true altitude were maintained through that portion of the flight.
Clearly, my logic in the above paragraph shows me to have my head on upside down!  The question is, what am I missing in the big picture to have drawn such an erroneous conclusion?  Does it have to do with where the temperature is warmer / colder than (adjusted) standard; i.e., at sea level or at the altitude at which the plane is located (my assumption)?  It has been suggested that I am thinking about Boyle’s Law and that is giving me an incorrect perspective on the situation.  But, even in free air, won’t colder air have increased density and therefore greater air pressure at the bottom of the air column compared to warmer air?
I’m totally confused and suspect I should just stay on the ground and taxi around!

The fact that you are aware that you are confused and acknowledge it, and that you are experiencing thoughts of staying on the ground give me reason to believe you may become a good pilot.  The other possibility is that you will have the introspection to decide that you will not make a good pilot, and you won't force a round peg into a square hole.  Either outcome is good.  Thanks for being you!

You're actually closer than you think:  it's not where the temperature is adjusted, it's where the pressure is adjusted.
The reason is that colder air above a ground pressure has a steeper pressure loss gradient with altitude than warmer air.  Because of its greater density near the ground, it needs less volume to make the same weight (pounds per square inch =pressure).
The column of air above a warmer place (at the same ground pressure) will be taller and have higher pressure at altitude.
Look at weather.  Cold fronts roll forward on the ground due to greater density, warm fronts ride up over cold air at altitude due to greater temperature.
To further understand this phenomenon one can compare pressure change differences to temperature change differences in passing fronts.  Pressure change differences occur gradually over many miles, whereas temperature change differences occur in a frontal passage over only a few miles.
Using the Gas Law P is proportional to Density and Temperature (Kelvin scale), one can see, with a passing front dropping temperature 30 degrees$^1$, we have (273+30)/273 =
an 11% difference in temperature at a similar local pressure$^2$.
So, local pressure gradient "stacking" with altitude, as confusing as it is, must be accounted for, as the altimeter only reads pressure.
$^1$ Celsius and Kelvin units are the same, 273 Kelvin = 0
Celsius, 303 Kelvin = 30 Celsius
$^2$ Even a hurricane pressure gradient can be as little as 960 mb/942mb over 100 miles, or around 1 percent!
What we need to know as pilots is the:

altimeter error relative to the ground pressure reported at a take-off/landing site based on deviation +/- from standard temperature

altimeter error relative to passing through a warm air mass into a cold air mass from temperature change and

altimeter corrections based on changes in reported ground pressure as we fly deeper into the cold air mass (they're bound to increase).

More reading here.

I made a nice picture for you:

Now, as we know, the air pressure can be thought of as the weight of the air above you.
We also know that temperature of any matter is simply the kinetic energy of the particles of that matter: The hotter something is, the more kinetic energy the particles of that matter have.
In atmosphere the kinetic energy of the gas molecules makes them bounce against each other, pushing them apart and expanding the gas. This expansion will also "push" the pressure gradients away from each other, so in hotter weather the pressure gradients are further apart from each other as shown in the crude presentation above.
A given volume of cold air is denser than the same volume of hot air, but in atmosphere the pressure gradients are also placed closer together in cold air.
This will manifest itself as the "from high to low, look out below".
 P.S. the atmosphere is a VERY complex system. Local atmospheric pressure is not in fact simply a product of the height of the air column above you. Vertical movements of the air and deviations from standard atmospheric lapse rate  also play a significant role in local atmospheric pressure. I personally found meteorology the most demanding and fascinating subject during my PPL studies due to the complexity of the subject :)


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Jet Fuel Flammability
Presently a  fueled passenger jet is a flying bomb.  Is there any hope in the near future of chemically  reducing the flammability of jet fuel on impact?

I may be wrong, but I don’t think it’s the impact which is the problem, but the fact the fuel enters into contact with fire, sparks, or high heat after an accident. And as long as we use combustion engines, we need something which can undergo combustion, in other words, can take fire. A change to completely different power sources would be needed.

B-52Gs used to burn water, but that was a special government program.

Jet fuel is not highly flammable like gasoline. It is basically kerosene or diesel fuel.

@jcaron whatever the energy source is, it brings the risk of uncontrolled energy release. The safe approach all over terra firma is to use electricity or gas from an external source - because one could (1) trivially limit the energy flow and (2) easy and quickly interrupt the energy flow. We still don't have the technology to power aircraft from an external source.

@Organic Marble. B52 and KC135 as well as several other early turbojet engine aircraft would inject water into the engines on take off. The water raised the humidity levels of air making denser and resulting in more thrust. The B52 and Kc135 had enough water to about 60 seconds of additional thrust during the take off roll.

@Jim that's what I was referring to.

Wrong starting point. Flying bomb it is not.
A passenger jet is way safer than a gasoline-powered passenger car in terms of flammability - both because of the fuel properties (see flash points for jet-a1 and gasoline) and because the engineering "safety vs expenses target" in aviation is WAY higher than in any land-rolling vehicle.
It is not a flying bomb. In a sense, it is a flying gas-station-sized fuel tank. Still dangerous, but not a bomb at any rate.
A vehicle needs a power source in order to operate. Should an energy source releases its energy in an uncontrolled manner, we do have a problem - no matter what the energy source is.
On the other hand, one should not expect much of improvement in the fuel properties.

It has to be able to burn.
It has to be liquid - for a number of reasons, coal is not an option in airplanes.
It has to have the maximum possible energy content.
It is already way safer than gasoline and only marginally less safe than diesel. While it is possible to ignite an open gasoline surface in air, it is pretty hard for jet fuel.

In short, the jet fuel is already almost as safe as chemically possible, with very little room for improvement.

Re, "coal is not an option" Aw, please! Can't we at least try? https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=9531e1f50b69600ab8701ac2e1306146be791849

@Ohm'sLawman The real danger in aviation is not coal, but the nucleat power. Experiments were made, it is doable, but imho the whole idea is better left alone.

@Ohm'sLawman now thar I read your link, ... fluidized coal IS explosive, it is a fine coal powder in compressed air. And for whatever reason, the technology does not see much land use either.

The only way to reduce the explosive effect of bursting a fuel tank and mixing the fuel with air is to inhibit sudden fluid motion of fuel inside the tank. In race cars this is done by stuffing the fuel cell with open-cell foam that acts like a big sponge. The fuel is capable of flowing out of this sponge by gravity fast enough to supply the peak requirements of the engine but the sponge "holds onto" the fuel during a sudden acceleration, as in a collision.

There was an attempt at this in the 80s. An additive

ICI's FM-9, a high molecular-weight long chain polymer, when blended with Jet-A fuel, forms antimisting kerosene (AMK)

and an old Boeing 720 was filled with it and deliberately crashed by remote control.
The results were...spectacularly bad...and AMK dropped out of sight.

More info at the Wikipedia article https://en.wikipedia.org/wiki/Controlled_Impact_Demonstration


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Are interlocked "traffic signals" possible/in use for taxiing?
I am a frequent viewer of the Youtube channel VASAviation which shows various interesting incidents regarding ATC. Recently there were two similar videos (first and second) where ATC directed a plane to take off while also directing other planes to cross the same runway.
I am not that familiar with the details of ATC, but I do know the world of railway signalling fairly well. There is a concept of interlocking there, whereby if a signaller sets a route for one train, that route is blocked for that train, and no further trains can be sent on any conflicting routes until the route has cleared. The signals on the track show "green"/"proceed" only if the route has been validly set. This is implemented historically through interlocked mechanical gears/levers and more recently by electrical (relay interlocking), electronic or software means.
In ATC, as far as I can see, there is no physical record of the clearances given to any plane. The controller just gives verbal instructions.
Wouldn't it be possible to create a sort of interlocked signalling system for taxiing at major airports, so that a controller has to set the route given to any particular plane in some control panel in the tower, which then would trigger signals on the field to become green, showing the pilot that it's safe to proceed? Verbal instructions could be retained for the specific routing, but they should be followed only after making sure the signals are green.
Would this be practical to implement? Has it already been implemented somewhere (and if so, why not at KJFK and KDCA?)

Railways are a bit more simple than airports, since you can assume that exactly one train is allowed in any one block at a given time. At an airport, the required separation is more diverse and depends on weather (more restrictive in low visibility), aircraft types (large aircraft may need to hold further from a runway) and what the aircraft is doing (multiple aircraft are allowed to be on a runway at the same time if they are taxiing - but not taking off/landing. Taxiing aircraft are also allowed to enter a runway behind an aircraft landing/taking off, but not in front of it).

You're referring to the railway signaling block system. Comparable systems exist for airports, with taxiway blocks managed by a central application, relying on taxiway centerline (TCL) lights progressive activation. In such application clearances and paths are all digitalized and use by the application, in addition of being transmitted by voice. Such application can exchange data with aircraft avionics.
Aircraft and vehicles are located using cooperative systems ADS-B, SSR, multilateration, ground sensors and radars. Compared to railway blocks, the airport system is more complex, vehicles can form queues, velocities must be managed, size may determine invalid paths and clearances, etc.
Two aircraft taxiing to the same runway, one is restricted, the taxiway centerline is prevented to illuminate in green past some limit:

(Source)
These applications are based on specifications agreed at ICAO level, and known as Advanced-Surface Movement Guidance and Control System (A-SMGCS) Services, described in Doc 9830. The specifications have four levels of increasing complexity.
For the case you cite: Conflicting clearances between a departing aircraft and a taxiing aircraft, this would be shown like this:

(Source)
This case is part of Airport Safety Support Service specifications:

The Airport Safety Support Service provides an automated alerting service to Controllers. It detects and triggers at least one of the following types of alert: RMCA, Conflicting ATC Clearances (CATC) and Conformance Monitoring Alerts for Controllers (CMAC). The Airport Safety Support Service is using the Surveillance Service, the Routing Service and the input of electronic Clearances.

There is an existing question: What is the Surface Management (SMAN) all about? answered by @DeltaLima, citing the application SMAN as implementing these specification (levels 3/4).
Such applications, which are part of ATC safety nets, are already deployed on some large airports:

Random examples found online: Abu Dhabi International, Nice, Liège, Charleroi, Zagreb,

A list of US airports on Wikipedia.

Generalization to large airports is in progress, e.g. in Europe within SESAR initiative. Deployment may be progressive, e.g. implementing levels 1/2, then 3/4, because hardware is required both in ATC premises and on the airport surfaces, this has a cost.
You can see a demo video here related to how stop bars are managed. A workstation at Riga airport (Latvia):

(Source)
Examples of critical alerts

ROUTE DEVIATION A mobile deviates from its cleared route on a taxiway (close to an active runway).

STATIONARY An arriving aircraft or mobile crossing a runway has stopped within the RPA and
does not move within a certain time period.

NO TAKE-OFF CLEARANCE An aircraft is cleared to Line-Up and it takes-off without a Take-Off Clearance.

NO LANDING CLEARANCE An aircraft is close to the runway without a Landing Clearance.

LANDING ON THE WRONG RUNWAY An arriving aircraft is detected to be aligned to a runway that differs to the assigned runway.

RED STOP BAR CROSSED A mobile crosses a RED stop bar (Intermediate Holding Point or AoR
boundary).

LINING-UP ON THE WRONG RUNWAY A departing aircraft is detected lining up on a runway that differs to the assigned runway.

RUNWAY INCURSION A mobile is detected entering, or predicted to enter, the RPA without a Land / Line-Up / Take-Off / Cross / Enter Clearance.

RUNWAY TYPE An aircraft is on a runway that is not suitable for the aircraft type.

TAXIWAY TYPE An aircraft is on a taxiway that is not suitable for the aircraft type.

RUNWAY CLOSED An aircraft has entered a closed runway.

TAXIWAY CLOSED An aircraft has entered a closed taxiway.

RESTRICTED AREA INCURSION An unauthorised mobile is detected entering, or predicted to enter, a restricted area.

HIGH SPEED An aircraft taxies with speed exceeding y knots (y=parameter).

(Source).


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IAS to TAS E6b giving me wrong answer
I am trying to work out TAS from IAS, having problems with it on MSFS.
the problem is as follows:
23000 FEET / 0 WIND / -19F (-28C) / IAS 304Knts / TAS (MSFS CORRECT) 426Knts / TAS (VIA E6b Calculator) 441Knts
(0 wind for testing of course).
How do I get the correct answer of 426Knts (any online calculator)?
P.S someone on an other forum helped me out but I still don't know why the E6b is giving me 441??
Many thanks!
The E6b calculator gives me this result

That online calculator appears to use equivalent airspeed in its calculation, but calls it indicated airspeed. And so it is invalid at higher mach numbers. In this case, an equivalent airspeed of 304 knots gives a true airspeed of 440.8 knots.
This online calculator appears to do it correctly.
Note that your question is about a specific online calculator, but a physical E6B makes various approximations and you should not trust it to be accurate at higher mach numbers either.


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What is, precisely, the function of far field monitor in ILS?
For what I have understood, far-field monitor (FFM) is composed by a set of antennas that receive the signal from the localizer, and check its integrity. The checking is made by extracting the DDM from the signal and comparing its value with some tolerance established by the ICAO standards. What I don't understand is: since DDM changes with the azimuth (i.e, the position in which the aircraft is collocated with respect of the runway), how can the monitor know the proper DDM value to check? Is there a set of antennas for every azimuth?
Let me explain with this picture**:
what are the meaning of those three black dots forming the FFM? In my opinion, they could be,for example: one FFM for DDM at -10°, one FFM for DDM at 0°, and one FFM for DDM at +10°. But I am not sure, because I can't find any source that confirm this.
Is there anyone that could give me an exhaustive explanation of what is a FFM, how is it phisically implemented and how it works exactly?

** Qu, C.. (2015). Research on Signal of Field Monitor of 7220A Localizer Beacon Subsystem of ILS. Open Journal of Antennas and Propagation. 03. 37-50. 10.4236/ojapr.2015.34005.

Per FAA Order 6750.16, the far field monitors are placed on the final approach course centerline, usually near the inner and/or middle marker beacons. Since this is on the centerline, the expected DDM is 0 (or very close to 0 if the siting is not exact). The azimuth of the aircraft may change, but the FFM itself is not moving and so its azimuth is constant.
Far field monitors are only required for category II and III approaches. There's not much point monitoring the localizer signal 10 degrees off course- any aircraft that far off course has long since gone missed!
The FFM is essentially a localizer antenna like would exist on an aircraft. It knows where it is an compares where it is to where the localizer signal says it is. If this disagrees by too much for too long, it sends a signal to the control tower and to the localizer antenna. Depending on the level of disagreement, this may disallow category II or III approaches or may even cause the localizer antenna to be shut down.
You can read the gory details in this report by Texas Instruments of their development of some early category III ILS approaches back in the 70s.

-10°/10° is the DDM linear sector for the localizer beam (DDM increases linearly from 0 at the center to 0.180 at 10°)

@mins Full-scale deflection is .155 DDM. The actual angle this corresponds to depends on runway length- the angle is set to whatever makes the full course width at the threshold 700 feet, or 6°, whichever is smaller. That means full-scale deflection (again at .155 DDM) is at most 3°, so I don't see how 10° could be .180 DDM and still be linear.

You're right, I misinterpreted this diagram from Annex 10. There is a range for linear DDM increase within the 10° sector, up to 0.180, the rest is required to be >= 0.180, but not linear, up to the 10°. So my comment should have been: This range, defined by ICAO, is where the DDM increases from 0 to at least 0.180.


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Is a flight for compensation legal for a Non-stop sightseeing trip?
I have been thinking about a scenario where I have a friend who has gotten sick and wants me to fly their aircraft with their family members for compensation since I am a commercial pilot. The flight consists of being non-stop, more than 25 NM away, and returning to the same airport with the purpose of sightseeing. Would this be legal?

Yes. If you're flying their aircraft there is no rule against you being compensated and this is a legal part 91 operation. It's no different than being hired to fly someone's business jet.
But you need to be careful here. The owner of the plane hiring you to fly his family around is fine. But the family members themselves must not be paying customers. That could essentially turn you plus the owner into an illegal charter operation.
If there are any complicating factors at all you would be wise to talk to the FSDO and/or an attorney before accepting such a job.


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Propeller Torque Calculation
Propeller torque is given as $Torque = c_p  * ρ * (\frac{ω}{2π})^2 * d_p^5$,
where $c_p$ is the torque coefficient, ρ is the air density, ω is the angular velocity, and d is the propeller diameter.
I want to calculate the torque but I do not know the value for the torque coefficient. Is there a way to estimate it? If the propeller diameter, pitch, RPM, etc are known, can this coefficient be calculated? I read in a paper that this coefficient has a typical value of 0.006. Is this value good enough for conceptual design?

Is your propeller fixed pitch or constant speed?
If it is fixed pitch and you are designing a small UAV of some sort, then I suggest you look at the UIUC Propeller Database.  There is a tremendous amount of propeller data taken in a wind tunnel.
If you are designing a larger aircraft, in particular one with a constant speed propeller, I suggest you find a copy of Roskam's Aircraft Aerodynamics & Performance book (direct from the author).
In the Appendix of this book, they have charts taken from something called the "Red Book" (because the cover was Red).  Ok, it looks like you can find the Red Book online, so you don't need to find Roskam's book.
Ham Standard Red Book
Although a bit old, this book is an industry standard source for propeller data.  You can use it for both constant speed or fixed pitch props.
If you don't want to use one of these sources, you'll need to use a blade element code to calculate the performance of a propeller of your own design.  Such codes include JavaProp, XRotor, QProp, CCBlade, etc.

You don't need to mount a prop on the engine to determine torque.  One can mount a blade with a known drag coefficient and run the engine up to a given RPM

fuel consumption is proportional to drag torque at a given RPM.

Once you know the drag of your blade, torque is calculated as drag × the distance of center of drag from the center of the hub.
You can derive the coefficient of drag from your prop by running it at the same fuel consumption rate as your known blade.  The torque will be the same:  drag × distance to the center of the hub.
Another way is to research the engine "horsepower" output listed as torque at a given RPM.  Prop drag torque (load) = engine torque output in a steady state.
From there derive prop drag by dividing out distance to center of the hub (from prop center of drag).
Finally, one can find coefficient of drag graphs for various airfoils and angles of attack here.  0.006 seems reasonable for an estimation of coefficient of drag using your $Torque$ calculation for prop load.

I don't think you can run a mono-bladed propeller without destroying the hub

@ok, try 2 blades

@sophit, it's fine as long as you add a counter balance.


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XFY-1 Pogo Contrarotating props alternative?
The Convair XFY-1 Pogo was a tail-sitter VTOL aircraft that used contrarotating props. I believe it was to counter the torque that would be produced if a single prop was used. Why couldn't the Pogo use the control surfaces on its tail to counter the torque instead of using contrarotating props? In other words, if the Pogo had been designed with a single prop, would it be possible for it to counter the torque using the control surfaces in the prop-wash (by creating a rolling moment opposite to the torque)? Could this be applied to a smaller aircraft such as the SkyTote UAV?

if the Pogo had been designed with a single prop, would it be possible for it to counter the torque using the control surfaces in the prop-wash?

Using the control surfaces blown upon by the propwash was the way to control it during takeoff and landing. With some bigger and skewed control surface it might have been possible to control it and to (partially) offset the torque even if it were built with one propeller only.
Anyway, why make things even more complicated than what they already were? A contra-rotating configuration made the slipstream (more or less) axisymmetric, disposed of any anti-torque mechanism and doubled the thrust without increasing the radius of the propeller.

When you advance the throttle, the torque (nearly) instantly increases.  However, the propwash does not immediately increase.  So your control authority using aerodynamic surfaces to counter the torque lags substantially.  When you are at idle, you have very little control authority -- and the torque is reacted by the landing gear contact with the ground.  This would lead to a highly nonlinear control system.  By using counter-rotating props, the torque self-cancels without any fancy control system or nonlinear effect.  It is a much simpler solution.

Yes, increasing the throttle gradually would have been necessary to give time to the propwash to reach the control surfaces and give them the possibility to generate enough lift. For sure at landing this is actually how it was controlled despite the delay and at the end it might have been possible also with only one propeller but, as said, why make things complicated?

There is a difference between controlling the vehicle this way -- when the torque is already cancelled vs. cancelling the torques and providing control.  I'm not disagreeing that propwash was use for control.  It certainly was.  However, I believe it would be implausible to use propwash exclusively to counter the torque of this vehicle.

Maybe with some bigger and skewed control surfaces might have been possible to partially cancel the torque out... But again, it might have been possible but definitely nonsense

@sophit, Please refer to the SkyTote UAV (https://en.wikipedia.org/wiki/AeroVironment_SkyTote ), which looks like a mini version of the Pogo (without the delta wing). In this case, wouldn't it be less complicated (mechanically) and weigh less if a single propeller was used with bigger control surfaces? Because I imagine the contra-rotating props would be more complicated, compared to using the servos which would be needed anyway. Also, can the propwash be utilized better by using control canards? I am trying to design such a UAV, so thank you for your advice!

The contra-rotating propeller needs only a couple of ball bearings and cogwheels. The bigger surface needed to counteract the torque would be heavier and generate additional drag. The anti-torque control would also be quite "nervous". A contra-rotating propeller is definitely the way to go.


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Is this an at-all realistic configuration for a DHC-2 Beaver?
As I learn more and more about aviation, I start noticing things.  The image below is clipped from The Long Dark, a disaster survival game centered around powerful geomagnetic storms.
At the inciting moment in the opening sequence, we get a view of the throttle quadrant of the De Havilland Beaver being flown by one of the two playable characters.  The pilot is Will MacKenzie, owner/operator of the family business: Jackrabbit Remote Transport, a single-plane bush flying concern.
The plane is airborne in a moderate-to-heavy snowstorm below overcast skies, at night, over mountainous terrain. It's an older float-equipped Beaver, with a radial engine (based on the sampled noises).
My gut says they've just passed top of descent as there is a brief moment of animation at this moment with the pilot's handing moving the throttle lever downward (or just taking his hand off of it, he's depicted as two-hands on the yoke at all other times in the scene).
The part that jumps out the most is that he's got the mixture at idle/cutoff, which I presume is because - as a solo operator - he's pinching every penny and trying to conserve as much fuel as possible.

Can an aircraft operate, even for just a few minutes, in this configuration? What are the concerns that the pilot should have about running the plane like this, even before everything electrical goes out?

Being in a Beaver at night in a snowstorm in mountainous terrain means you have a couple of minutes to live anyway, so you might as well have the mixture set to shut down the engine; same result lol.

Not likely as the engine has no fuel going to it at this point with the mixture at idle cutoff.  A DHC-2 Beaver is also a normally aspirated airplane so manifold pressures that high are unrealistic as well, operable engine or not.  And I certainly hope that they are flying in amphibious version of the DHC-2, as opposed to only a floatplane, and they are going to make an instrument approach into a land airport.  Landing in water at night is extremely difficult (thought it can be done in emergencies using parachute flares for illumination).  Also, most seaplane bases do not have instrument approaches available for them, making it all the more difficult. Realistically, I think John K is right - night flying over mountainous terrain, not on an instrument flight plan in marginal weather in a snowstorm is a recipe for suicide.
A more plausible scenario:  the developers and 3-D artists, who I’m going to guess are aviation illiterate, found a photo of a DHC-2 cockpit, most likely in a cold and dark setting and made a 3-D model of it without any understanding of how a pilot would actually operate the thing.  The good news? 99.99% of the players won’t notice and/or care.

Honestly, I'm impressed that they got the actual inside of a DHC-2 instead of a 172 or something.

@WilliamWalkerIII -  Yeah, in a game where an aurora can make wolves aggressive and cause lethal current to flow in downed power cables, realism is not the game designer's chief mission.  That they used an appropriate bush airplane and got the right cockpit image for it, that's a big win.  I'm not going to haggle over whether the controls are in the right position.  BTW The Long Dark is a very fun game; I agree with the designer's choices.  There are flight sims for when more accuracy is wanted.

@WayneConrad Yeah, the reason I'm asking all this stuff is because I'm planning to re-create the doomed flight for Twitch, and I'll be using said flight sims. XD

@WilliamWalkerIII Nice!

If the mixture control is at cutoff, then all fuel flow to the engine is... well, cut off. That means the engine is going to shut off from lack of fuel. Now, some carbureted engines can run for a few seconds on just the fuel left in the carburetor, but that's probably going to actually cost the pilot fuel, since crashing the airplane is highly likely to puncture the fuel tanks and spill the rest of the gas all over the terrain.
What's more likely is that whoever created the game just found a picture of some plane's dash, and modeled the in-game cockpit after that, without bothering to figure out the actual proper position of any controls beyond the throttle.

Unless this is an amphibious float equipped Beaver, or any other float plane, you wouldn't be flying at night. There are no lighted water landing areas, and you wouldn't see obstacles in the water, and it would be very difficult to judge your height during the landing phase. Unless you are suicidal!

It is amphib, actually. whether or not that's realistic is it's own thing, but the flight begins out of a land-based hangar...


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How to make ourselves more visible to other aircraft?
What are the best practices in air to help others see our aircraft?

transponder maybe?

Transponders, ADS-B (which, honestly, is pretty much just an outgrowth of transponders) and exterior lights have already been mentioned. I'd like to add one more thing: speak up!
You've probably got a microphone right in front of your mouth, which is ultimately connected to a radio transmitter which is hopefully tuned to a frequency monitored by nearby aircraft.
To help make yourself more visible to other aircraft, press the transmit button and give your location and intentions, to let them know at least one place where they should look.
As a real-world example, another pilot did this the other day as I was in the air, saying something like "XX Radio, SE-XXX on downwind 21, for touch and go". My instructor took the opportunity to quiz me about where they should be given that, and they were pretty much exactly where I expected them to be. Not only did we now know where they were (position and, by inferrence, approximate altitude), which we could have known by looking for other traffic, but we also knew what they were planning to do. In this case, there was no risk of a traffic conflict between us, but you never know who else is out there.
Unless the traffic situation is congested, or there's something like emergency traffic going on, the occasional radio call with your position and intentions can do little but help others.

+1 for self announcing at non-towered airports.  I've surprised others by calling out I was #3 for landing.  #1 had never announced, #2 had heard me calling in and had seen #1 but thought it was me. I was both of them obviously.

@CrossRoads I'm not sure what you're saying; are you saying it'd be a good strategy to deliberately give misleading information? If so, then we are in disagreement, even if it doesn't materially change the situation (in the case you mention, because there is no #1 and #2 in line for landing while you report being #3). There's probably an applicable rule, too. If, say, I am entering the traffic pattern and someone calls out being #3 and I can only see one aircraft and not hear any others on the radio, it could certainly throw a wrench into my plans until I'm able to confirm what's going on.

I was aware of the 2 planes ahead of me - I saw them both in the pattern. The 2nd plane (with it turns out was a student pilot & instructor) in the middle was not aware of the 1st plane in line. When I called out that I was #3 for landing, they were were surprised, and started looking and soon located the plane in front of them. So no misleading - just me being  more on top of the situation than others.

Ah - I see the typo in my earlier comment, "was" vs "saw".

Depends on the situation.  For day operations, a minimum of an operational anti-collision light system must be used, but in general it is difficult to beacons or strobes in daylight prior to spotting the aircraft as a whole.  Night ops are much easier where one can use navigation and anti-collision lighting to readily be seen and identify other aircraft at a distance.
The Aircraft Owner’s and Pilot’s Association (AOPA), in conjunction with the FAA and other regulating bodies, instituted a safety improvement program called Lights On Look Out, which makes use of the aircraft landing lights when operating within Class B, C and D airspace at or below 10,000 ft ASL.  This is a very effective way to make the aircraft more visible to other pilots, provided the aircraft configuration can accommodate this.  Some aircraft actually make use of pulsing or strobing landing light modes  intended for day use.  It is also extremely effective to make use of landing lights when maneuvering or flying in confined spaces like mountain valleys for easier identification and collision avoidance.
Another way to make ones self more readily visible is to be aware of blind spots which all aircraft have, depending on the configuration.  High wing aircraft block a great deal of the upper field of view just as low wing aircraft make it difficult for a pilot to see what’s under them.  Care therefore must be taken when turning or maneuvering to first clear blind spots around the aircraft by rolling slightly, scanning the airspace you are about to turn towards, then turning.  Aircraft therefore should exercise extra caution when descending to land for aircraft below them which may not be immediately visibile, yet in danger of overtaking and colliding with them.  Proper, established pattern entry techniques should be used when possible to allow other pilots in the pattern to easily identify aircraft entering or leaving the pattern and pilots should have descended to pattern altitude within 3 miles of the airport.  This is especially true during operations from untowered airports where all traffic may not be using or transmitting on the CTAF.  Proper radio calls should be used at said untowered airports to allow other traffic to more readily identify the block of airspace you are in and visually acquire you.

Have your lights on: Red beacon light on the fuselage or tail, white light on the tail, Red & Green navigation lights on the wings, strobe lights on the wings, and your landing light(s).

Being equipped with ADS-B is also good. Other aircraft with ADS-B In will see you on their electronics and be looking for you.


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What to do when moisture forms on the helicopter's canopy in a weather front?
Moisture has condensed on the canopy of your helicopter as you fly through a weather front – what should you do?

That won't happen "flying through a front" where the temperature of the plexiglass is at at or warmer than the ambient air - you just get drops forming and streaming back.  What has happened to me though, is condensation when climbing into a warm humid inversion on a sunrise clear sky departure where the surface temperature was much cooler than in the inversion.  On my airplane which has a sliding bubble canopy, the outside of the canopy fogged up suddenly at about 200 ft agl as the cool plexiglass hit warmer humid air and it was like the canopy was covered in wax paper.  A bit alarming initially.  I just used the attitude indicator to stay right side up, helped by the opaque blue of the sky above, until it started to stream and clear up on its own after a minute or so.


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Winglet design and airfoil selection
I'm currently in the process of designing a winglet for my low speed aircraft in xflr.
While researching about winglets I read in a Boeing article that if the baseline outboard wing is relatively lightly loaded, as on the 747-200, the potential benefit of tip devices can be greatly reduced. I don't understand the logic behind this statement.
Also what would be the optimal airfoil selection for the winglet? How would the chord, thickness, camber, etc. affect the weight and drag reduction due to the winglet?
And would the geometric twist affect the performance of the winglet?
Any other tips for winglet design would be greatly appreciated.

A highly loaded wingtip makes the tip vortex stronger. The rotation of the vortex makes the apparent direction of the wind at the tip face inboard. The winglet toes out into this wind allowing its lift vector to rotate slightly forward which creates thrust or reduces drag, whichever you prefer. A lightly loaded wingtip makes a weak vortex, reducing the effect of the winglet. Designing one is as complex as designing a wing, so I'll let someone else take it from here.

@Pilothead You have it exactly right, with a minor quibble.  Yes they make thrust the same as a sail boat's sail.  Which is why they were originally called "tipsails".  However while they are toed out to optimize AOA, the lift vector itself is a function of the inward angle of the tip flow, lift being at 90 degrees to the airflow, not AOA.  Almost nobody actually mentions the "sail" aspect of a winglet, just that there is some mysterious drag reduction.

@JohnK: You are right about the sail analogy, however, this is just a different manifestation of the effect a winglet has on the flow. It spreads out the vorticity gradient so the lift vector is less inclined backwards (which is almost equivalent to saying that the winglet contributes a forward-slanted component, right?).

@Zaber - Your information is correct. In fact, some Japanese carriers experimenting with winglets found there where no fuel savings (even possible losses) on short haul routes within Japan. To be efficient, winglets need to be "tuned" for a specific speed and load.

The comments explain the logic behind a winglet well, so I will focus on the remaining questions:

what would be the optimal airfoil selection for the winglet?

As a first rule of thumb, continue with the wing airfoil. A cambered winglet will be most efficient, because winglets are only beneficial if they produce lift. How much? This depends on the ratio of wing tip chord to winglet root chord. Ideally, there should be no break in the spanwise distribution of circulation, so the product of local wing chord and local lift coefficient should be the same at the transition and taper out towards the winglet tip.

would the geometric twist affect the performance of the winglet?

Yes: The incidence must be chosen such that the desired lift coefficient is trimmed at the operating point (which is the cruise condition in case of airliners). Twist will only be needed when the planform differs a lot from the elliptical distribution. When flying with a high wing loading (again, just as airliners do), be sure to include the effects of aeroelastic deformation: They can be quite severe around the wing tips in cruise.

I'll provide a partial answer.  What they are saying is related to the fact that the thrust generated by the winglet is only high enough to exceed its own drag penalty when the wing is producing strong vortices.  The vortices are stronger as you get slower and AOA goes up.  There is some crossover point as you speed up where the weakening vortices don't produce more thrust than the winglet's own drag and they no longer produce a net benefit.
The result is that they are only worthwhile on an airplane that cruises "slowly" from an indicated airspeed perspective.  Generally, airplanes that cruise at low indicated airspeeds are those that cruise above 30000 ft, where they may only be flying at 2x stall or a little more.  This is why you only see winglets on jet airliners as a rule (yes there are exceptions but not many, and the weird turned up wing tips on the draggy slug CL-415 water bomber aren't winglets at all).
I would only put a winglet on a low speed aircraft if its intended cruising speed is close to its best L/D, like a glider.


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Why is there an area of different density right at the nose of a plane going supersonic?
A normal subsonic enough, but still compressible flow will compress when it gets to the planes nose. But in supersonic flow, there won’t be this compression. There will just be a shockwave which turns the flow instead of the high pressure turning the flow. Granted, this depends on nose angle and the speed of the plane.
The shockwave itself has different properties, but those should be fairly even throughout the whole shockwave.
But if you look at the very tip of the nose in this picture, you will see a bigger black area, AKA different density.

Why is there this little area of more black/different density? The shockwave should be constant density, right?
Originally, I thought maybe this is because the angle of the nose was too high for an oblique shock to form, so a normal shock formed instead, but the nose seems to be at a fairly low angle so I don’t think this is the case.

The main thing you are seeing here is an artifact that the image is a sum of a bunch of 3D layers -- not just a 2D slice.
The nose of the airplane is a cone, so the flow structures happen in 360 degrees.  So, you're seeing a thin slice through the middle, but also through all the layers in-between.

I see. So, basically it’s just an artifact because of the way the image is taken?